Scratchbuilding Treehawk from Gerry Anderson's Terrahawks

Back to INDEX by David Sisson See also Sci-Fi & Fantasy Models Issue 7 July/August 1995

In the classic television series 'Thunderbirds' one of the most memorable ideas was the fact that several of the International Rescue vehicles launched into the air via concealed exits, a swimming pool, a moving cliff face and a house with a great big hole down the centre. When Terrahawks appeared Gerry once again used the same idea, but this time I got the impression that he was having a bit of a laugh!
We had the mighty Battlehawk navigating its way up a terribly narrow passageway before taking off through a Mansion house and Hawkwing launching underwater via a spinning Lake!
Then we had Treehawk, the regular short-range space vehicle, which like its name implies comes out of the centre of a tree. Not too interesting compared to the others but equally silly when you realise just how big this tree would need to be! Being possibly the fattest tree on Earth isn't that cleaver a disguise in the middle of a forest and it would be hard to launch any secret spacecraft with all the tourists and documentary film makers around taking pictures of the great big thing! Still the offshoot of this idea was to restrict the overall design, creating a narrow sleek bullet-shaped craft. Because of this it is probably the least interesting of the Terrahawk vehicles, although like Battlehawk I thought Steven Begg's preproduction artwork was a far better looking idea.

Although I do now like the Terrahawk models I don't want to find myself building them over and over again in the future as I have with my Thunderbird fleet. The general idea is to try and build them correctly the first time round and the best way of doing that is to build them to same size as the originals, making this model 22 & 1/2 inches long.

The first task was to draw up the blueprint and luckily I had a photocopy of the original working drawing to guide me. I then just had to spend a few hours comparing it to pictures of the finished model and altering it in a few areas to match.
To start the model I formed the basic hull shape in Balsa wood. As the hull has a simple triangular cross-sectional view and flat sides for over two thirds of its length I quickly blocked it out just using three pieces of 1/2-inch Balsa and some internal triangular supports. All I then had to do was round off the edges and flatten the top for the cockpit area.
The nose section was then carved from a collection of pre-cut Balsa sheets which were glued together to form a solid mass. This was done by first cutting out the side profile from a single sheet of wood that became the centre of the nose. The spaces on either side were then filled in with horizontal layers of Balsa cut to the shape of the top view plan. This gave me the general shape required so again I just had to round off the edges which with soft Balsa doesn't take that long. In fact the problem with Balsa is that it's often too easy to remove more wood than you need to, which is why many model makers prefer harder woods. Unfortunately the opposite effect can then manifest itself as often not enough material is removed and the models can end up looking a bit square and blocky.

With the basic shape now formed I would usually make plaster moulds and cast the model in fibreglass, however as I had no intention of ever building a duplicate I decided not to waste any time and just use this master pattern as the final model. So the soft wood was given three coats of SP113 epoxy resin and then rubbed down with wet & dry paper to create a nice tough smooth finish.

The next step was to form the top section and wing areas in mostly 2mm Plasticard with the recessed spaces having to be cut out of the hull.
The wings themselves were made from two layers of plastic with the fins being cut from Perspex and shaped on my beltsander.

I spent a great deal of time on the wings and the hinges, which were made from brass parts, as they had to move up and down with the minimum of gaps showing.
It was only after I had finished that I realised it was all a waste of time as it would have been far easier to have detachable wings that could be set in the open or closed position.

Detail inside the wing recesses had to be invented and was simply kit-bashed from two sets of identical parts from Tamiya tank kits and the Airfix girder bridge.
I don't really like using hardwood, but at this stage it was necessary because I needed to use it to make the two side fairings. These parts were created from one-inch dowel that I split down the middle and glued to the sides of the hull, then P38 filler was used to blend the parts into the rest of the fuselage. These hardwood fairings took a lot of effort to shape and when they did finally look correct I then had to drill out and remove the front sections as they form part of the undercarriage.
Picture left to right : The master for the cockpit cabin, the final transparent moulding, the rear undercarriage domed footpad and the front two undercarriage feet recently drilled from the fairings.

The ragged holes in the fairings were smoothed over and reformed with car filler. Then the area was carefully covered over in electrical tape, more filler was applied and the wood pieces that had just been removed were pushed back into place. After the filler had set the surplus bits were cut away and the wooden footpads prised away from the surface of the tape - that had acted as a barrier to prevent the filler adhering to the hull.

The undercarriage parts could now be sanded down to their correct shape whilst always checking that they still fitted perfectly into the recesses. The wooden parts were coated in resin, sanded again and finally spray-painted.

The resin coated wood hull was given several coats of spray filler and sanded down, any minor pinholes or blemishes would show up at this stage and could be fixed. The wings were now carefully attached and the gaps around the edges, especially next to the hinges, were filled to achieve a close fit for the moving parts. The cockpit area was given some detail and outfitted with a pilot figure in line with the original design. (In later episodes the cockpit became a two-seater) The transparent window area was heat formed from 0.75mm plastic, glued in place with two-part quick setting epoxy and blended into the rest of the upper structure with car filler.
On the original model I believe the transparent moulding extended back to the start of the wing section. This is often one of the different techniques between professional and amateur model makers. Amateurs tend to come from the 'Airfix' school of thought and just build the visible window areas, trying to insert bits of transparent material into gaps in the models surface while attempting not to get glue marks on everything. Professionals often mould the whole area from transparent material and then just mask off the windows during the painting stage. If you can mould the larger parts its a much easier way of doing things.

The last major piece to be built was the large engine bell at the rear of the model. To make this part I firstly glued a smaller rough basic shape to a wood base to form the core, then cut the outline shape from a piece of 2mm plasticard which had a pin fixed to the centre which could be inserted into a hole drilled in the top of the core. Wet plaster of Paris was then applied to the core and the plastic stencil rotated to form the desired shape. This plaster master wasn't good enough to use itself so I then heat moulded a sheet of Plasticard around it and used this to cast a duplicate in P38 car filler. This filler master could be sanded and reshaped to the correct dimensions, and when it was done a plaster mould was made and the final part produced as a thin fibreglass casting.
The only kit parts on this model are here in the open rear end, four Airfix Space Shuttle solid rocket booster nozzles and an engine bell from the Revell Lunar Lander.

The model was now sprayed with cellulose motorcar paints, Signal Orange (correct) and Silver Fox - which is wrong because it's too light and I've had to heavily weather the model to try and correct it.
Panel lines were drawn in using a standard black biro and I've lightly scored the surface to catch some of the weathering.

The Terrahawk markings were photographs, taken of the emblem printed on the back of a record sleeve, which I had retouched to correct for colour defects. As the photo paper isn't as thin as a decal I tried to minimise its extra height by applying masking tapes to form corresponding holes in the paint surface.
The only other marking on the model come from the decal sheet of the Airfix 1/24th scale Harrier.

The last problem was fitting the undercarriage, as I didn't want to set it in either the up or down position. I decided to construct the legs from an assortment of brass tubes that can be pushed together or taken apart at will. However the model looks far more interesting with the legs down so that's its usual appearance.

When the original model was first filmed it was quite clean but for later episodes they really dirtied it up - even more than this replica appears here in these slightly contrasty pictures. Metal hooks have been fitted, at the front (just in front of the cockpit) and rear, for attaching to wires for display purposes.

All photographs by David Sisson

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